Background

Vancomycin-resistant Enterococcus faecium (VREfm) is one of the leading causes of severe healthcare-associated infections. In China, the prevalence of VREfm has remained low (average <5%) in the past decades. However, the surveillance systems revealed that the prevalence of VREfm has increased. We aim to investigate the epidemiological and genomic characteristics of VREfm in China.

Methods

We collected 20747 non-redundant E. faecium isolates from inpatients across 19 hospitals in six provinces between Jan 2018 and June 2023. VREfm was confirmed by antimicrobial susceptibility testing. The prevalence was analyzed using a changepoint package in R. Genomic characteristics of 311 VREfm were explored by whole-genome sequencing. Five representative isolates that harbored vanA-plasmids were sequenced by the Illumina PacBio RSII system. Plasmid conjugation was performed using fusidic acid-resistant Enterococcus faecium BM4105 as the recipient. Transconjugants were selected on BHI agar plates supplemented with fusidic acid (50 mg/L) and vancomycin (8 mg/L), and verified using MALDI-TOF and PCR for vanA.

Results

5.59% (1159/20747) of E. faecium isolates were resistant to vancomycin. The prevalence of VREfm increased in Guangdong province from 5% before 2021 to 20%-50% in 2023 (p<0.0001), but not in the other five provinces. Two predominant clones before 2021, ST17 and ST78, were substituted by an emerging clone, ST80, from 2021 to 2023 (88.63%, 195/220). All ST80 VREfm from Guangdong formed a single lineage (SC11) and were genetically distant from the ST80 VREfm from other countries, suggesting a regional outbreak. All ST80 VREfm in SC11 carried a new type of plasmid harboring a vanA cassette, which was embedded in a Tn1546-like structure flanked by IS1678 and ISL3. However, no conjugation-related gene was detected and no transconjugant was obtained in the conjugation experiment, indicating that the outbreak of ST80 VREfm could be attributed to clonal transmission.

Conclusions

We revealed an ongoing outbreak of ST80 VREfm with a new vanA-harboring plasmid in Guangdong, China. This clone has also been identified in other provinces and countries, foreboding a risk of wider spreading shortly. Continuous surveillance is needed to inform public health interventions.